Lapping films are used to work a particulate abrasive material against the surface of a workpiece until the surface has an exceedingly fine, well controlled finish. Generally, it is desirable to attain a very smooth surface finish while obtaining and retaining a high degree of dimensional control, so that the resulting product will conform to very precise finish and size standards. The lapping of surfaces from their original state to the final finish is a progressive operation, involving the use of a series of abrasives ranging from relatively coarse abrasive particles at the beginning through successively finer sizes in the end. The results secured depend upon a number of factors, such as the properties of the abrasive employed, the pressure with which the abrasive is forced against the workpiece, the pattern of movement preserved in the contact of the workpiece with the abrasive particles and other considerations.
The lapping film is manufactured by coating an abrasive slurry on a backing and drying and/or curing the slurry. Generally, the abrasive slurries are in the form of slurries wherein the diamonds form a discontinuous phase and a liquid, such as an organic solvent or binder precursor, forms the continuous phase. Diamonds have been used as the abrasive particles in lapping films because of their hardness.
In coating from a slurry, the diamonds and/or other superabrasive particles will be subjected to gravitational forces and settle out of the continuous phase. The rate of settling depends on a number of factors, including the size and density of the superabrasive particle, the viscosity of the continuous phase, and most particularly the aggregation state of the superabrasive particles. It is desirable to have a majority of the superabrasive particles dispersed to their primary size and maintain this size distribution for an extended period of time. Additionally, agglomeration leads to larger abrasive particle size in the finished products that can scratch the surface of the workpiece.
The present invention solves the above-identified problems by utilizing a class of polymeric dispersants in the slurry to aid in the dispersion of micron and sub-micron super-abrasive particles in organic solvent systems. In a slurry of the invention, the abrasive particles are dispersed in the continuous phase as individual particles and do not re-agglomerate. Additionally, the abrasive particles resist settling out of the continuous phase due to the diminished influence of gravitational forces on single particles relative to agglomerates of these particles.